I can't actually think of a job where I was relaxed the whole time. I don't think I would want to do that job. When I break into a cold sweat when I'm reading, I think, 'Oh good. That's what's supposed to be happening.
So, for the most part, I really like when I read a scene that scares me and makes me sweat a little bit, thinking about doing it. That's usually a good sign to me.
I think every script I read has something that sends me into a state of panic but that usually makes me want to do it.